Field of the Invention
This invention is directed to a method and apparatus for separating overlapped sheet metal panels, which have been spot-welded together, with a minimum of damage and distortion to the panels, thus permitting any one or all of the panels to be reused.
The majority of truck cabs and bodies and greater than 95% of all automobiles sold in the United States since the late 1980's utilize the unibody construction. The unibody is assembled from stamped or formed sheet metal panels which are spot-welded or resistance-welded together in overlapping relationship. The spot-weld or resistance-weld is formed by a controlled electrical current applied to two or more metal panels while the panels are pressed together, resulting in a small circular area or spot of the contiguous panels being bonded together. The diameter of the spot and the quality of the weld will be influenced by changes in the electric current, the nature of the sheet metal panels, the amount of pressure applied to the overlapping panels, etc.
The unibody construction utilizing a plurality of spot or resistance-welds between overlapping sheet metal panels is ideal from a manufacturing standpoint. However, repair of a damaged unibody vehicle can be labor intensive particularly when one or more damaged sheet metal panels must be replaced. Correct panel replacement can become very time consuming. The approved method of repair requires that all damaged spot-welded panels be removed and replaced with new panels spot-welded to the original undamaged sheet metal panels in the original factory relationship.
Spot-welded panel separation requires the removal from at least one of the panels of the series of spot-welds bonding the overlapping panels together. Due to numerous problems, however, the panels frequently remain attached after the spot-welds have been removed. For example, each spot-weld is commonly removed by drilling or milling through the overlapping sheet metal panels at each spot-weld location. However, if the drill bit or mill is slightly off-center with respect to a spot-weld, a thin line on one side of the spot-weld will remain, continuing to secure the overlapping sheet metal panels and preventing their separation. If a drill bit or mill is used which has a diameter smaller than the diameter of the spot-weld, a thin circular line of the spot-weld remains, preventing separation of the overlapping sheet metal panels. Occasionally, there is a pattern of smaller welds called spot-weld spatter surrounding a spot-weld, resulting in the overlapping sheet metal panels remaining welded together even after the spot-weld has been fully removed.
Also, sealer or adhesive between the panels applied to restrict water or air flow between the panels and paint or primer between the panels applied to restrict rust or corrosion act as an adhesive, bonding the overlapping sheet metal panels in areas surrounding the spot-welds. The overlapping sheet metal panels remain bonded together by the sealer, adhesive, paint or primer even after the spot-welds have been removed.
Separating the overlapping panels which continue to be bonded together due to the incomplete removal of the spot-weld, the spot-weld spatter between the panels and/or the bonding by the sealer, adhesive, paint or primer, requires excessive force frequently resulting in damage not only to the panel being replaced but to the other panel or panels adjoining this panel. Moreover, the time required to separate these overlapping panels and at the same time minimize damage to the panels is substantial.
An object of the present invention is to provide a method and apparatus for separating overlapping spot-welded sheet metal panels in substantially less time while minimizing damage and distortion to the panels.
A further object of the present invention is to minimize the damage to the overlapping spot-welded sheet metal panels while being separated and, at the same time, drastically reduce total panel replacement time compared with prior art methods.